This invention relates to a semiconductor tester system for testing integrated circuit devices in wafer form.
FIG. 3 of the drawings illustrates a semiconductor tester system of generally conventional structure. Such a tester system is typically located in a clean room. The tester system includes a wafer prober 10 having a frame 12 in which a vacuum chuck 14 is mounted for movement along two horizontal axes (X and Y) and a vertical axis (Z). A ring carrier 18, which is a metal ring equipped with a latching mechanism 20, is supported above the prober frame by a ring carrier support structure 22, which typically includes three angularly spaced support points. For the sake of simplicity of illustration, the two support points shown in FIG. 3 are illustrated as if they were at an angular spacing of 180.degree. although they would not in fact generally be at an angular spacing of 180.degree.. The ring carrier 18 is latched to the support structure 22.
A generally annular probe card stiffener 26 is provided at its outer periphery with latch elements 28 for engagement with the latching mechanism 20 of the ring carrier 18. A generally annular probe card 30 rests on the probe card stiffener. The probe card has an outer area at which contact pads are exposed at the upper surface of the probe card and it has an inner open area from which probe tips project downward toward the vacuum chuck 14. The probe tips are connected to the contact pads of the probe card by conductive traces of the probe card.
A test head assembly 32 is positioned above the ring carrier 18. The test head assembly is in contact with the ring carrier 18 and is latched thereto. The test head assembly typically has a mass of at least 150 kg. Most of the weight of the test head assembly is carried by a manipulator 34, but a significant part of the weight of the test head assembly is carried by the ring carrier 18.
When the latch elements 28 of the probe card stiffener 26 are engaged with the latching mechanism 20, the contact pads of the probe card engage spring-loaded contact elements 36 which project downward from the test head assembly and provide electrical connection between the test head assembly and contact pads of the probe card.
For testing an integrated circuit device in wafer form, the wafer 40 is placed on the vacuum chuck 14 and is held in place by partial vacuum applied to the lower surface of the wafer. The vacuum chuck may be moved horizontally to position the contact pads of the wafer vertically below the probe tips and then moves upward and delivers the wafer to a test station in which the contact pads of the wafer engage the probe tips, for making electrical contact with the integrated circuit device, and stimulus and response signals are communicated between the test head and the wafer by way of the contact elements 36 and the conductive traces of the probe card.
It is important that the plane of the contact pads of the wafer 40 be parallel with the plane of the probe tips of the probe card 30 to ensure that the probe tips enter electrically conductive contact with all the pads of the wafer under test when the vacuum chuck is displaced to the test station. For this purpose, at least two of the support points of the ring carrier support structure 22 are individually adjustable in height for adjusting the orientation of the ring carrier 18 relative to the prober frame 12.
Because the weight of the test head assembly 32 is shared between the ring carrier 18 and the manipulator 34, vibration of the floor on which the prober frame and manipulator rest can lead to independent vibration of the test head assembly and ring carrier. Since the test head assembly is latched to the ring carrier, this independent vibration can cause distortion of the ring carrier. Further, the horizontal relative movement of the probe card and the wafer can lead to misalignment of the probe tips with respect to the pads of the device under test, impairing the accuracy of the test to a significant extent, and to erosion of the probe tips, reducing the useful life of the probe card. Moreover, the manipulator includes moving parts which shed debris, which is undesirable in a clean room environment.